Sterilizing reusable trays provides a long-term return on investment.

Photo courtesy of Proptek

Proptek’s injection molded propagation trays and containers are designed to produce quality plants, reduce labor and increase profits. But with great results comes great care. Paul Greenly, sales director at Proptek, explains the importance of disinfecting reusable trays for a long-term return on investment.

Produce Grower: Why is it important to clean trays, particularly injection molded ones?

Paul Greenly: Injection molded trays can be reused many more times than Styrofoam and thermoformed trays. Sometimes these can’t be reused at all! This does mean that when you get the trays back from customers, they need cleaning and sterilizing so disease doesn’t carry over to the next seeding.

PG: Is this an expensive or complicated process?

Greenly: Injection molded trays make this very easy and straightforward, with a very low-cost input. The trays’ reusability more than makes up for the higher cost of tray and the slight cost of the cleaning process. This makes it very worthwhile in purchasing a tray that costs a little more upfront and is worth getting back from farmers.

PG: Can you describe how trays are cleaned?

Greenly: Cleaning is most commonly done with steam with trays stacked in a confined space such as a shipping container. Steam is good as it penetrates well and has no potential chemical residues. There are five steps growers should take:

1. Using a steam generator, pipe-in steam at 170° F (approximately 75° C).

2. Have a backup system that cuts off the steam if the temperature gets to 180° F to prevent prolonged overheating and trays/containers shrinking, warping or melting.

3. The time to get to your temperature of 170° F will vary depending on whether it is winter or summer or the first, second or third load of the day. Start timing from when the container reaches temperature and not when you turn it on. We recommend that containers stay at temperature for one hour or more after it has reached 170° F.

4. If possible, install a fully automatic temperature control and timing system with a built-in emergency stop.

5. Open the doors as soon as possible after the time is up. Moisture escapes better as the product cools down and the product ends up drier — this is important if it is going straight into a new production cycle, as wet product means soil will stick to it, etc.  

A very important last point! Lots of leaks with steam coming out is no bad thing, as this prevents damage to the container or even explosions.

PG: Are other trays capable of doing this?

Greenly: No — at least not easily or well. This is down to the material of other trays. Styrofoam is too porous: trying to sterilize it is very difficult. It is also a very good insulator and getting the heat all the way through all the trays is very difficult. Thermoformed trays, on the other hand, are thin and weak. This means they can’t take the temperatures needed very well and can warp at low temperatures and become unusable.